Bow frame chain saw



NOV. 18, 1952 c PRATT 2,618,298

' BOW FRAME CHAIN SAW Filed D80. 2'7, 1949 2 SHEETS-SHEET l Nov. 18, 1952 'H PRATT Y 2,618,298

130w FRAME CHAIN SAW Filed Dec. 27. 1949 2 SHEETS-Sl-IEET 2 Patented Nov. 18, 1952 UNITED STATES PATENT OFFICE 2,618,298 Bow CHAIN SAW "Henry C. Pratt, Philadelphia, .Pa., assignor .to Henry Disston and Sons, Inc., Philadelphia, Pa.; a-corporation'of Pennsylvania Application December 27, 1949, Serial No. 135,230

This invention relates to chain saws and more particularly to an improved guide means for the cutting chain; a a

More specifically the invention relates to chain saws of the type wherein the chain is supported upon the guide means with the exception only of that part of the chain which engages the drive sprocket, and a primary object of the invention is to provide a chain guide for saws of this type having generally improved characteristics as hereinafter more particularly described.

Another object of the invention is to provide a guide rail of the stated type composed of one integral piece ofrnetal thereby eliminating joints, interruptions, and variable curvatures in the'rail; and maintaining a constant operating'relationship between the rail and the chain.

Another objector the invention is to provide a guide rail and chain assembly of the bow type'of which the rail element may be readily produced by stamping or other equally inexpensive operation, and wherein further the separate sections of the prior conventional guide rails are eliminated:

Afu-rt'her object of the invention is to provide a rim which is of such a width and thickness that in backing up the cutting chain and following the chain'into the cut; it cannot be'bound orpinched' by closure of the out behind the cutting chain.

Still another object of the invention is to pro vide' a guide railtha't will'produce maximum centrifugal action in the chain under operating conditions whereby the-chain may be forced by the centrifugal force outwardly from the guide rail'so as to reduce friction between the rail and the chain.

A further objcc't of the invention is'toprovide a guide-rail designed so that centrifugal force acting upon themovin'g chain will serve to prop erly tension the chain under operating conditions,

the guide rail still maintaining its primary functidn o-f guiding thechain in its longitudinaltrave'l over'a predetermined path;- In this phase the vide a guide rail so constructed and so mounted on the body of the saw that adjustments there oi for the purpose of compensating for chain elonga tion are obtained by adjustment of the wh le guide rail, with respect to the engine frame; there by maintaining a constant operating relationship between the rail and the chain. r

Still another object of the invention is to pro= vide a novel chain guard for the chain which will function also as a mediurnfor conferring lateral stability upon the guide rail structure;

A still further object of the invention is to provide a chain saw constructed so as to facilitate installation and removal of thecutting mam,

The invention further contemplatesa'g'ui eraif of simple form and relatively light weigh in conjunction with said rail a guardstruc ur which will function to confer stability -and'ri'g1d' ity upon the rail structure. I i r g The invention will bemore rea'di ly understood by reference to the attached drawings; wherein Fig. 1 is a side 'elevational'vie'w of aphainsaw made in accordance with theinvention; Fig. 2 is an enlarged side'elevation'al perspect M view of the saw Wlthth'e guard andcover'platef removed to show the chain sprocket am ne; manner in which theguide rail is secured to the,

main frame; n Fig. 3 is a view in perspectiveo'f'th'e combined guard and cover plate; I

Fig. 4 is a sectional view on the'line'4"4, Figrl; Fig. 5 is a sectional view on the line '.i5;l*i'g:' 2; and

of the guide rail'd'etached from'the's'aw structure;

With reference tothe drawings; the saw therein illustrated comprises an internal combustion gine indicated generally by the reference meral I, the motor frame being provided w h" two handles designated respectively by the reference numerals 2 and 3. Associated with the" handle 3 is a throttle 4 by means of whichtlie' operation of the motor may be controlled.

Journaled in the frame and operatively co'n nectedwith the motorl is a chain sprocket 5,

fad

see Fig. 2, and this sprocket engages the cutting chain 6 which is supported and guided over the major portion of its length by a guide rail 1. In the present instance the chain link are provided with spaced ears 8, see Fig. 4, which straddle the edge of the rail 1, intermediate portions 9 of the chain engaging the edge surface of the rail, as illustrated, so that an adequate running connection is established between the chain and the rail.

The guide rail 1, as best shown in Fig. 6, is in the form of an open frame or bow with a well rounded outer end portion of ample radius. The inner end of the rail is provided with a pair of parallel slots II and I2 for reception of studs l3 and 14 through which the rail is secured to the motor frame. By means of these studs the base portion l5 of the rail is clamped solidly against a face I3 of the said frame as hereinafter more fully described. The guide rail 1 also comprises a slot l! in the base portion thereof which extends parallel to and between the slotted openings II and i2, and in assembly this slot l'i receives a rectangular boss I8 which projects from the face l6 of the frame and which carries a screw I9, the inner end of the screw being rotatably supported in the boss. A block 2| is threaded on the screw I9 and, being prevented from rotation as shown in Fig. 5, may be adjusted along the axis of the screw by turning the latter. In assembly the block 2| engages the guide rail 1 at the inner end of the slot IT and it will be apparent that by manipulation of the screw I9 and adjustment of the block 2! the rail I may be moved outwardly away from the sprocket 5 to thereby obtain a proper operative relation between the rail and the chain.

In the present instance the base part of the guide rail 1 is clamped between the face [6 of the frame and the inner face of a cover plate 22, see Fig. 3. This plate is provided with apertures 23 and 24 for passage therethrough of the rail-retaining studs l3 and Id, and has on its inner face projecting flanges 25 which bear against the confronting face of the rail so that when nuts 26 and 21 are tightened on the studs against the outer face of the plate 22 the butt end of the guide rail 1 will be clamped solidly to the motor frame.

The cover plate 22 not only houses the sprocket 5 and the inner ends of the chain and guide rail, but also, through the medium of an extension 28, functions as a guard for those portions of the chain which pass in proximity to the handle 2 and an outboard support for the guide rail '1. As shown in Fig. 4 the extension 28 is of channel form embracing the chain and is provided at its outer end with an inwardly projecting boss 29 the outer end of which is adapted for engagement with the proximate face of the guide rail 1. The boss 29 is apertured as indicated at 3 and this aperture in assembly registers with a slotted opening 3! in the guide rail 7. A bolt 32 passes through the registering hole and slot and with an associated nut 33 rigidly secures the outer end of the extension 28 to the guide rail. The plate. 22 and its integral extension 28 are rigid, being formed, for example, from cast aluminum, so that the arm 28 functions not only as an efficient guard for the upper run of the chain but also confers a high degree of lateral stability on the guide rail structure. It will be noted that the extension 28 terminates at a point slightly beyond the longitudinal center of the guide rail so as. to allow for cutting over and above the full capacity of the depth of the rail and if circumstances require.

It will be noted that the outer end of the screw l9 extends beyond the cover plate 22 so that if adjustment of the guide rail 1 is required such adjustment may be effected by release of the screw 32 and the studs [3 and I4 and subsequent rotation of the screw I9. Removal of the cover member 22 may be accomplished by removal of the retaining screw 32 and of the nuts 26 and 21 of the studs 13 and M. Following removal of the cover 22 chain 6 may be readily removed from the saw structure by backing the block 2| on the screw l9 to release the guide rail 1 and subsequently removing the chain from both the rail and the sprocket 5. It is obvious that the rail 1 may be removed by the same operation.

It is to be noted that the open bow guide rail 1 approximates a circle at its outer free end. As a result a considerable centrifugal effect is developed in the rapidly moving chain. This centrifugal force is utilized for two primary ends, first to reduce friction between the guide rail and the chain, in that the chain tends by centrifugal action to leave the edge of the rail, and secondly, to dynamically tension the chain for optimum operating efiiciency. For these desirable ends, the guide rail is designed to produce maximum centrifugal action in the chain.

In assembling the saw the guide rail is adjusted so that under static conditions the chain is free on the rail. Under operating conditions the aforesaid centrifugal action takes effect to dynamically tension the chain, the said force tending to draw the chain away from the rail edge. Through this expedient necessity for the conventional spring tensioning means has been eliminated, as also has the necessity for maintaining substantial pressure between the guide rail and the chain. In the present instance the rail exerts no tensioning pressure upon the chain and functions merely to guide the chain in the desired path and to maintain the chain in proper operative connection with the sprocket 5. Since undue slack in the chain is taken up by adjustment of the guide rail as a whole with respect to the sprocket 5, it will be apparent that the operative relation between the guide rail and the chain remains constant. Also, by reason of the fact that the rail is composed of an integral piece of metal the chain finds a continuous and uninterrupted guide, free from joints and interruptions. Obviously, the integral construction and plain form of the guide rail materially simplify the manufacturing process with respect to this part of the saw assembly, and make possible production of the guide rail by simple stamping operation from an integral piece of metal of suitable guage.

A one piece guide rail of the character described above has certain material advantages over rails composed of several parts spliced to-, gether, It affords, for example, a rail which is substantially lighter in weight than rails of the other type by reason of the absence of the additional elements required in rails of the spliced type for securing the parts together and for re-v enforcing the joints. A one piece rail of the character of the applicants is also less subject to distortion than one made of an assembly of parts by reason of the fact that the integral rail contains no joints that might work loose. When the joints of a spliced rail loosen they frequently produce obstructions on which the chain may catch thereby tending to impede the progress of the chain and the rail. Also, in practice, foreign matter such as pitch, sap and oil tends to work into even minute spaces between the sections of a spliced rail where they are riveted, bolted, Welded or otherwise secured together,the ultimate result being a tendency to produce looseness in the joints. Obviously, this also is avoided in a rail composed of one integral piece. As previously set forth the integral guide rail affords a substantial economy in that it can be stamped from flat metal, whereas a guide rail made of a number of pieces requires additional material for splicing the pieces together and also involves the labor necessary to putting the parts of the rail together.

I claim:

1. In a chain saw, a cutting chain, a substantially flat guide member providing at its edge a support for the chain and on which the chain over substantially its entire length is constrained to travel in a closed smoothly contoured path, and a chain-driving sprocket at the inner end of said guide member, the chain guiding edges of the member diverging from the sprocket and merging into the opposite sides of an approxi- 6 mately circular are at the outer end of the member, said are embracing an angle materially in excess of 180 degrees and containing the major extent of the chain-guiding edge of the guide member.

2. A chain saw according to claim 1 wherein the said chain guiding edge extends into close proximity to the opposite sides of the sprocket.

HENRY C. PRATT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

